SI (Systéme International) units:
-
Length: the meter (m) is defined as the distance light travels in a vacuum in 1/299,792,458 sec (note that this is truly universal: in principle it can be determined by anyone, anytime, anywhere in the Universe).
-
Mass: the kilogram (kg) however is still based on the International Prototype Kilogram in Paris and the derived standard kilogram standards held by governments around the world.
-
Time: the second (s) is defined today as the duration of 9,192,631,770 periods of the radiation of two hyperfine levels of the ground state of the cesium 133 atom.
-
Amount of substance: the mole (mol) is defined as the number of atoms in 0.012 kg (defined, so sig figs not restricted) of carbon 12 atoms.
-
Temperature: the kelvin (K) is defined as 1/273.15 of the thermodynamic temperature of the triple point of water.
-
Electric current: the ampere is defined as the the current which carries one coulomb (6.24146 x 1018 times the charge on an electron or proton) of charge through a conductor in one second.
You should know (memorize) and be able to interconvert the prefixes in the table below:
SI Prefixes
Prefix |
Symbol |
Magnitude |
tera- |
T
|
1012
|
giga- |
G
|
109
|
mega- |
M
|
106
|
kilo- |
k |
103 |
base |
|
100 |
deci- |
d |
10-1 |
centi- |
c |
10-2 |
milli- |
m |
10-3 |
micro- |
 (or mc)
|
10-6 |
nano- |
n |
10-9 |
pico- |
p |
10-12 |
fempto- |
f |
10-15 |
© R A Paselk
Last modified 30 January 2015